"No-smoking areas may provide some reduction in the level of exposure of individuals to environmental tobacco smoke. However, the reduction may be marginal or trivial," the researchers said.

Environmental tobacco smoke or second-hand smoke, is a complex mixture of more than 4000 chemical compounds generated from smoking or burning tobacco products.

The scientists measured atmospheric nicotine in 17 social and gaming clubs in and around Sydney. They found levels varied but, on average, if a person moved from a smoking to a non-smoking area it would reduce the amount of nicotine inhaled by about 53%.

Toddlers and passive smoking?

In a separate study in the journal, scientists in the U.S. said smoking outdoors reduced toddlers' exposure to tobacco smoke. But it did not completely protect them because environmental smoke lingers in dust and on household surfaces.

"To our knowledge, this is the first study to document that surfaces, dust and air are contaminated in homes of smokers with infants," said Dr Georg Matt of San Diego State University in California.

The scientists compared amounts of environmental tobacco smoke in 49 homes with children between one and two years old. Non-smokers lived in 15 of the houses and the remainder were occupied either by people who smoked indoors or those who tried to protect their children by smoking outside.

After taking samples of dust, indoor air and household surfaces, Matt and his team found levels of environmental tobacco smoke were five to seven times higher in the homes of smokers to tried to protect their children than in houses occupied by non-smokers and three to eight times higher if the parents smoked indoors.

They said the findings were worrying for young children who spend much of their time indoors and are often close to contaminated surfaces such as carpets, floors and tabletops.